Single-pixel camera captures high-quality, encryptable images

The sequence shows the difference between the original image (obtained with a wrong key) and the unencrypted one (Image: UJI)

In the crowded digital camera market, camera makers are continually pushing pixel counts higher and higher to attract consumers who have been led to believe that, the more pixels, the better the image. Proving that this is not necessarily the case, a team of researchers from Spain’s UJI (Universitat Jaume I) Optics Research Group (GROC) has developed a sensor of just one pixel with the ability to record high quality images.

CCDs

The CCD (charge-coupled device) sensors at the heart of today’s digital cameras record the electrical signals generated via the photoelectric effect in a large number of image points, known as pixels. This allows the light falling on a specific point on the sensor to be converted to a digital value. The CCD was invented in 1969 at AT&T Bell Labs by Willard Boyle and George E. Smith, with the two eventually recognized for their achievements by the Royal Swedish Academy of Sciences, which awarded them the Nobel Prize for Physics in 2009.

Nowadays, digital cameras with CCD sensors boasting millions of pixels are commonplace and, with the dimension of the sensors always the same (typically, 24.7 mm2), it is commonly believed that the higher the pixel count, the better the image quality. This is, however, not necessarily the case, with other factors – most notably, the quality of the lens – also playing a major role.

Single-pixel camera

The new single-pixel sensor developed by the UJI team goes against this common belief using a technique dubbed ‘

ghost imaging’, which is based on the sequential recording of the light intensity transmitted or reflected by an object illuminated by a series of

noisy light beams. This

noisy light is what we observe, for example, when a piece of paper is illuminated using a laser pointer. To generate the necessary

noisy light beams, the device uses a small one-inch LCD screen whose properties and features can be modified using a computer. The LCD screen is similar to home video projectors, but in miniature.

Using the single-pixel camera, the GROC team has successfully captured 2D object images such as the UJI logo and the face of one of the maids of honor from Picasso’s 1957 reinterpretation of the famous Las Meninas painting.

Encryption

The researchers have also demonstrated a secure way to distribute the high-quality images captured by the single-pixel camera over the internet using a method they say had not previously been used for image encryption. By transmitting the image as a simple numerical sequence, the image can be retrieved, but only by those who know the hidden codes used to generate the noise patterns that were used to create the image.

The team also hopes to use the same technology to capture images of internal biological tissues, which can be more difficult to view using pixelated devices, such as those commonly used in today’s digital cameras. Using this technique for image encryption, the researchers say, will improve secure image transmission, product authentication, whilst keeping information hidden from undesired viewers.